It is known to record sound oscillations mechanically on a planar signal carrier so that the recording extends along a spiral groove having closely adjacent turns, the sound oscillations having an upper frequency limit of approximately 20,000 Hz and the information being recorded as three-dimensional undulations, or deformations, on the surface of the recording groove. It is also known that it is possible, by the so-called pressure scanning technique, to mechanically scan much higher signal frequencies -- up to several MHz -- which are required for playing back video recordings. The spatial recording in the groove in this case is effected according to the depth, or hill-and-dale, recording technique.
Because of the broad frequency range to be covered in storing video signals, for example when storing a moving picture, the scanning of such a video recording must be effected with playback speeds which are substantially higher than those for the conventional sound recordings, and which can be as high as 1500 rpm for a 200mm diameter record.
It is obvious, however, that the recording of such video signals by mechanically, electrodynamically or electrostatically controlled recording devices cannot be effected at the same speed as playback because the member producing the deformations corresponding to the signals in the recording groove could not possibly, because of its mass inertia, follow the high frequency oscillations to be recorded, the frequency of which extends up to 4 MHz. A picture record copy, or the matrix therefor, is thus produced by an intermediate recording of the signals, as is done in the manufacture of ordinary phonograph records, for example on a magnetic carrier which is then played back at a speed which is reduced about 10 to 25 times so that with an upper frequency limit of about 4 MHz for the signals to be played back, the recording instrument must be capable of producing perfect recordings at frequencies up to about 160 or 400 kHz, respectively.
In spite of the greatly reduced recording speed, this upper frequency limit is still extremely high for an instrument which must be capable of producing mechanical deformations in the recording groove of a signal carrier. Even particularly good instruments and those designed for special purposes at the present have an upper recording frequency limit of approximately 30 to 40 kHz.
A stylus has now been proposed for video recordings which is capable of recording in a much higher frequency range, up to 400 kHz. But even with such a stylus, intermediate storage is still required in order to be able to record frequencies up to 4 MHz.
Efforts have been made to develop processes in which the intermediate storing can be eliminated. This is possible, for example, in the known recording technique by means of laser or electron beams in which photolacquer layers are exposed and subsequently etched. The difficulty arising in this process is mainly that it is necessary to record a track which can later be mechanically scanned. For this purpose it is known to precut the track mechanically and to subsequently expose it to laser beams. This dual recording, however, produces substantial difficulties because of the high groove density involved, which is up to 280 grooves per mm.
It has been discovered that a pure laser beam recording is possible, with all the advantages inherent in such a process, in that a type of dual peak recording is produced as it is known in the sound film art.